1. Field of the Invention:
This invention relates to a lubricant and surface conditioner for formed metal surfaces, and more particularly, to such a lubricant and surface conditioner which improves the mobility of aluminum cans without adversely affecting the adhesion of paints or lacquers applied thereto, and also enables lowering the dryoff oven temperature required for drying said surfaces.
2. Discussion of Related Art:
Aluminum cans are commonly used as containers for a wide variety of products. After their manufacture, the aluminum cans are typically washed with acidic cleaners to remove aluminum fines and other contaminants therefrom. Recently, enviromental considerations and the possibility that residues remaining on the cans following acidic cleaning could influence the flavor of beverages packaged in the cans has led to an interest in alkaline cleaning to remove such fines and contaminants. However, the treatment of aluminum cans generally results in differential rates of metal surface etch on the outside versus on the inside of the cans. For example, optimum conditions required to attain an aluminum finefree surface on the inside of the cans usually leads to can mobility problems on conveyors because of the increased roughness on the outside can surface.
These aluminum can mobility problems are particularly apparent when it is attempted to convey the cans through single filers and to printers. Thus, a need has arisen in the aluminum can manufacturing industry to modify the coefficient of static friction on the outside surface of the cans to improve their mobility without adversely affecting the adhesion of paints or lacquers applied thereto. The reason for improving the mobility of aluminum cans is the general trend in this manufacturing industry to increase production without additional capital investments in building new plants. The increased production demand is requiring can manufacturers to increase their line and printer speeds to produce 20 to 40 percent more cans per unit of time. For example, the maximum speed at which aluminum cans may be passed through a printing station typically is on the average of about 1150 cans per minute, whereas it is desired that such rate be increased to about 1400 to 1500 cans per minute or even higher.
However, thoroughly cleaned aluminum cans by either acid or alkaline cleaner are, in general, characterized by high surface roughness and thus have a high coefficient of static friction. This property hinders the flow of cans through single filers and printers when attempting to increase their line speed. As a result, printer misfeeding problems, frequent jammings, down time, and loss of production occur in addition to high rates of can spoilage.
Another consideration in modifying the surface properties of aluminum cans is the concern that such may interfere with or adversely affect the ability of the can to be printed when passed to a printing or labeling station. For example, after cleaning the cans, labels may be printed on their outside surface as well as lacquers may be sprayed on their inside surface. In such case, the adhesion of the paints and lacquers is of major concern.
In addition, the current trend in the can manufacturing industry is directed toward using thinner gauges of aluminum metal stock. The down-gauging of aluminum can metal stock has caused a production problem in that, after washing, the cans require a lower drying oven temperature in order to pass the column strength pressure quality control test. However, lowering the drying oven temperature resulted in the cans not being dry enough when they reached the printing station, and caused label ink smears and a higher rate of can rejects.
Thus, it would be desirable to provide a means of improving the mobility of aluminum cans through filers and printers to increase production, reduce line jammings, minimize down time, reduce can spoilage, improve ink laydown, and enable lowering the drying oven temperature of washed cans. Accordingly, it is an object of this invention to provide such means of improving the mobility of aluminum cans and to overcome the afore-noted problems.
3. Description of the Invention: Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term "about".
In accordance with this invention, it has been found that a lubricant and surface conditioner applied to aluminum cans after washing enhances their mobility and improves their water film drainage and evaporation characteristics as to enable lowering the temperature of a drying oven by from about 25 to about 100.degree. F. without having any adverse effect on the label printing process. The lubricant and surface conditioner reduces the coefficient of static friction on the outside surface of the cans enabling a substantial increase in production line speeds, and in addition, provides a noticeable improvement in the rate of water film drainage and evaporation resulting in savings due to lower energy demands while meeting quality control requirements.
More particlarly, in accordance with this invention, it has been found that application of a thin organic film to the outside surface of aluminum cans serves as a lubricant inducing thereto a lower coefficient of static friction, which consequently provides an improved mobility to the cans, and also increases the rate at which the cans may be dried and still pass the quality control column strength pressure test. It has also been found that the improved mobility and drying rate of the cans depends on the thickness or amount of the organic film, and on the chemical nature of the material applied to the cans.
The lubricant and surface conditioner for aluminum cans in accordance with this invention may be selected from water-soluble alkoxylated surfactants such as organic phosphate esters; alcohols; fatty acids including mono-, di-, tri-, and poly-acids; fatty acid derivatives such as salts, hydroxy acids, amides, esters, ethers and derivatives thereof; and mixtures thereof.
The lubricant and surface conditioner for aluminum cans in accordance with this invention preferable comprises a watersoluble derivative of a saturated fatty acid such as an ethoxylated stearic acid or an ethoxylated isostearic acid, or alkali metal salts thereof such as polyoxyethylated stearate and polyoxyethylated isostearate. In addition, the lubricant and surface conditoner for aluminum cans may comprise a water-soluble alcohol having at least about 4 carbon atoms and may contain up to about 50 moles of ethylene oxide. Excellent results have been obtained when the alcohol comprises polyoxyethylated oleyl alcohol containing an average of about 20 moles of ethylene oxide per mole of alcohol.
Further, the lubricant and surface conditioner for aluminum cans in accordance with this invention may comprise a phosphate acid ester or preferably an ethoxylated alkyl alcohol phosphate ester. Such phosphate esters are commercially available under the tradename Gafac PE 510 from GAF Corporation, Wayne, New Jersey, and as Ethfac 136 and Ethfac 161 from Ethox Chemicals, Inc., Greenville, S.C. In general, the organic phosphate esters may comprise alkyl and aryl phosphate esters with and without ethoxylation.
The lubricant and surface conditioner for aluminum cans may be applied to the cans during their wash cycle, during one of their treatment cycles, during one of their water rinse cycles, or more preferably, during their final water rinse cycle. In addition, the lubricant and surface conditioner may be applied to the cans after their final water rinse cycle, i.e., prior to oven drying, or after oven drying, by fine mist application from water or volatile non-inflammable solvent solution. It has been found that the lubricant and surface conditioner is capable of depositing on the aluminum surface of the cans to provide them with the desired characteristics. The lubricant and surface conditioner may be applied by spraying and reacts with the aluminum surface through chemisorption or physiosorption to provide it with the desired film.
Generally, in the cleaning process of the cans, after the cans have been washed, they are typically exposed to an acidic water rinse. In accordance with this invention the cans may thereafter be treated with a lubricant and surface conditioner comprising an anionic surfactant such as a phosphate acid ester. In such case, the pH of the treatment system is important and generally should be acidic, that is between about 1 and about 6.5, preferably between about 2.5 and about 5. If the cans are not treated with the lubricant and surface conditioner of this invention after the acidic water rinse, the cans are exposed to a tap water rinse and then to a deionized water rinse. In such event, the deionized water rinse solution is prepared to contain the lubricant and surface conditioner of this invention which may comprise a nonionic surfactant selected from the afore-mentioned polyoxyethylated alcohols or polyoxylated fatty acids. After such treatment, the cans may be passed to an oven for drying prior to further processing.
The amount of lubricant and surface conditioner to be applied to the cans should be sufficient to reduce the coefficient of static friction on the outside surface of the cans to a value of about 1.5 or lower, and preferably to a value of about 1 or lower. Generally speaking, such amount should be on the order of from about 3 mg/m.sup.2 to about 60 mg/m.sup.2 of lubricant and surface conditioner to the outside surface of the cans.